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The 911 emergency call system

is intended to give individuals a simple, easy-to-remember, routinely available number that can be used to reach an appropriate public safety provider during any life-threatening situation.[1]


Using a landline, wireless, mobile telephone, or voice over internet protocol (VoIP) system, a caller dials 911 and the call is routed to a communications provider facility that automatically forwards the call to a public safety entity such as a PSAP. Next, the call taker/dispatcher talks to the caller to determine the nature of the emergency and to determine the necessary first responders, while working to send (or dispatch) the appropriate first responders to the location. According to the National Emergency Number Association, there are more than 6,000 PSAPs nationwide, at a county or city level, that answer more than 240 million 911 calls each year.

Once a 911 caller places an emergency call, the communications provider receives and routes the call to the appropriate PSAP. The system used to route the call depends on the type of telephone used to make the 911 call.

For a call placed from a landline, a router in the communications provider's central facility receives the 911 call and accesses the Automatic Number Identification database to associate the identifier with the phone number to determine the caller's address. Then, based on the location information, the communications provider's Master Street Address Guide database identifies the appropriate PSAP to receive the call. When a cell phone is used, the location information is typically provided to the PSAP through either cell tower triangulation technology or by Global Positioning System technology.

When using VoIP, where calls are carried over digital subscriber lines, cable modems, or other Internet access methods, the caller needs to register the address of the VoIP device in advance. Current telecommunications and PSAP technology associate the voice and data transmission with the identifier and location databases and, based on the caller's location, routes the call to the appropriate PSAP.

When the caller's phone number, address, and voice are routed to the appropriate PSAP, the call is automatically delivered with the phone number and location. The trained 911 call taker/dispatcher assists the caller and inputs information into additional IT systems and infrastructure to begin the emergency response. For example, the call taker/dispatcher may enter information into a computer-aided dispatch system. These systems automate the call-taking process, provide questions and responses for various scenarios, and send the first responders.

Based on the information put into the system by the call taker/dispatcher, the computer-aided dispatch system interfaces with other systems for identification and address, ascertains the nature of the assistance needed, and transmits the information to the appropriate first responder. To provide assistance to the first responder, the call taker/dispatcher may also be able to use geospatial tools and systems that provide information on utility placement, government facility types and locations, property plats, mapping data, and aerial photographs. In addition, call takers may use criminal justice information databases, Internet access, automated vehicle locator to select the closest first responder, and radio and telecommunications services to share and receive information as the situation warrants.

While a PSAP is to be available on a 24-hours, 365 day-a-year basis, an emergency operations center, as noted, is typically only activated during an environmental emergency or special event. It provides a single location for key decision makers from state, local, and federal agencies and multiple jurisdictions to gather and to react to events too complex or too large for regular offices or communications centers or single government agencies or jurisdictions to handle. From a single location, the officials can support on-scene incident commanders (such as fire, police, and emergency medical personnel), prioritize the allocation of resources, collaborate on strategy and tactics, and manage the fiscal and social consequences of an incident.



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